The present invention relates to a method and a device for controlling mobile robot systems employing a control station and a plurality of mobile robots.
Recent developments of factory automation techniques offer mobile robot systems which employ a control station and a plurality of mobile robots, each of which travels and performs a task according to an instruction given by the control station. FIG. 2 is a block diagram showing the functional configuration of this kind of mobile robot system. In FIG. 2, C designates the control station; and R1 through Rn designate the mobile robots. Control station C and each one of mobile robots R1 through Rn communicate by means of wire communication or radio communication. The instructions are given to control station C by a host computer UC or an operator OP. These instructions may be sequentially supplied to control station C at short intervals which are shorter than the operation time required for the mobile robots to perform the tasks. Therefore, the instructions are stacked in control station C. When a mobile robot Rk having no task occurs, the oldest instruction among the stacked instructions is selected and transmitted to the mobile robot Rk. The robot then starts to carry out the task designated by the instruction. When a plularity of mobile robots, each having no task, occur simultaneously in the system, control station C instructs the mobile robots to determine the best travel route and to evaluate the route. Each robot then searches the possible travel routes through which the mobile robot can travel to the work point at which the task is to be carried out, and selects the best travel route which is the most preferable, for example, the possible travel route having the shortest length, or the possible travel route generating the lowest loss of the power of the robot. Each robot further calculate the losses which are generated when the robot travels through the best travel route and determines the evaluation value based on the calculated results. The evaluation result obtained by each robot is transmitted to control station C. Control station C selects one of the robots, which transmits the most preferable evaluation value.
In the above system, however, the operation efficiency of the system may often be low due to the above-described instruction selection in which the instructions are selected according to the sequence of the instructions and the older instruction is selected earlier. For example, suppose the following case occurs:
(1) Mobile robots R1 through R3, having no task, are waiting for instructions in the system as shown in FIG. 3. PA1 (2) The instructions corresponding to tasks W1 and W2, which are to be performed at the points respectively indicated by "W1" and "W2" in FIG. 3, are stacked. PA1 (3) The instruction of task W1 is older than the instruction of task W2. PA1 (a) When mobile robots having no task exist in the system and tasks not completed are remaining, the control station instructs the mobile robots to evaluate the remaining tasks. PA1 (b) The mobile robots evaluate the remaining tasks and report the evaluation values to the control station. PA1 (c) The control station sequentially selects the one of the combinations of the mobile robots having no task and the remaining tasks based on the evaluation values of the combinations in such a manner that the combination representing the better evaluation value is selected earlier, and assigns the task of the selected combination to the mobile robot of the selected combination.
In this case, control station C instructs mobile robots R1 through R3 to determine the best travel route and to evaluate the route for executing the task W1 because the instruction of task W1 is older than the instruction of task W2. When the evaluation values are transmitted from mobile robots R1 through R3 to control station C, the control station then instructs the task W1 to one of the robots which presents the best evaluation value. In this manner, task W1 is carried out earlier than task W2. However, task W2 should be carried out before task W1 in the case shown in FIG. 3, because the all mobile robots R1 through R3 are closer to the work point of task W2 rather than the work point of task W1.